a. Field of the Invention
The present invention pertains to integrated circuits and specifically to input pads used on integrated circuit dies.
b. Description of the Background
Standardized circuitry blocks are commonly used in today's very large scale integrated (VLSI) circuits. The circuitry blocks may have a specific functionality and may be combined with other blocks to create specialized integrated circuits for many types of applications. Examples of standardized circuitry includes memory modules, processor modules, and input/output (I/O) pads.
I/O pad is a term used to define the bonding surface of an integrated circuit die. In many cases, an I/O pad may include some passive or active circuitry for various functions. The standardized I/O pads may include various functions through which an incoming or outgoing electrical signal may be conditioned or changed prior to entering or exiting the integrated circuit die. The I/O circuitry may reside underneath the actual bonding surface on the top layer of the integrated circuit.
Many different circuits are commonly used in I/O pads. For example, such circuits may provide ESD protection, filter an incoming signal, or provide matching impedance for connecting circuitry. If the functions were not provided in the I/O circuitry, the same functionality would have to be provided somewhere else in the integrated circuit.
As manufacturing techniques improve for integrated circuits, more circuitry can be placed in a specific area. For example, the amount of circuitry that may be placed beneath the bonding surface of an I/O pad is increasing as manufacturing techniques improve. Further, the need for many functions for signal preparation of incoming signals is likewise increasing.
It would therefore be advantageous to provide an I/O pad that comprises ESD protection and adjustable impedance. It would be further advantageous if the I/O pad were suited for a differential input, provided a minimum of capacitance, and provided common mode rejection.